Corrosion-resistant low-emissivity coatings

ABSTRACT

A corrosion-resistant low-emissivity coating is provided. The low-emissivity coating comprises, in sequence outwardly, a corrosion-resistant inner infrared-reflective layer, a transparent dielectric middle coat, and an outer infrared-reflective layer. The outer infrared-reflective layer consists essentially of silver and the corrosion-resistant inner infrared-reflective layer has a different composition than the outer infrared-reflective layer. Also provided are methods for depositing coatings of this nature, as well as substrates bearing these coatings.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority to utility U.S. patentapplication filed Jun. 7, 2004 and assigned Ser. No. 10/862,770, whichin turn claims priority to provisional U.S. patent application filedJun. 10, 2003 and assigned Ser. No. 60/477,302, the entire disclosure ofeach which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention provides coatings for glass and other substrates.More specifically, this invention provides low-emissivity coatings. Theinvention also provides methods for depositing coatings of this nature,as well as substrates bearing these coatings.

BACKGROUND OF THE INVENTION

Low-emissivity coatings for glass and other substrates are well known inthe present art. Typically, they include one or more infrared-reflectivelayers each positioned between two or more transparent dielectriclayers. The infrared-reflective layers reduce the transmission ofradiant heat through the coating (e.g., by reflecting infraredradiation). These infrared-reflective layers typically compriseconductive metals, such as silver, gold, or copper. The transparentdielectric layers are used primarily to reduce visible reflectance andto control other coating properties, such as color. Commonly usedtransparent dielectrics include oxides of zinc, tin, and titanium, aswell as nitrides, such as silicon nitride.

In most cases, each infrared-reflective layer in a low-emissivitycoating comprises silver. Silver is the most commonly usedinfrared-reflective material because it provides high electricalconductivity (and hence low-emissivity), high visible transmission, andneutral color. A drawback of using silver for each infrared-reflectivelayer is that silver lacks mechanical and chemical durability. Silverlayers are very soft and thus limit the mechanical durability ofsilver-based coatings. Silver layers are also particularly vulnerable tobecoming corroded. Thus, great care must be exercised to preventsilver-based coatings from being damaged. For example, considermanufacturing periods (e.g., prior to and/or during assembly of coatedsubstrates into IG units). During these periods, coated substrates arefrequently subjected to relatively harsh conditions. For example, theconditions associated with handling, shipping, and washing can causesilver-based coatings to become scratched or otherwise abraded. Duringmanufacturing periods, coated substrates are also commonly exposed toair, moisture, and other chemicals, all of which can cause silver tobecome corroded. Thus, when pure silver layers are used in alow-emissivity coating, the overall durability of the coating tends tobe less than ideal.

Attempts have been made to enhance the durability of infrared-reflectivelayers. For example, some have replaced the inner and outer silverlayers with layers of a more durable reflective metal. Others havereplaced the inner and outer silver layers with layers of a silver alloycomprising a small amount of a more durable reflective metal. Forexample, alloys of silver and palladium have reportedly been found tocreate infrared-reflective layers with greater durability than puresilver. These alternatives, however, have largely been rejected in themarketplace, as they are predominately viewed as yielding unacceptablyhigh emissivity. Therefore, pure silver is typically used for eachinfrared-reflective layer in a low-emissivity coating, notwithstandingits mechanical and chemical vulnerability.

The properties of an infrared-reflective silver layer depend upon thesurface over which it is deposited. For example, a silver layer can begrown to have particularly low emissivity by depositing the silver layerdirectly over a film of pure zinc oxide. Thus, it is a widespreadpractice in the art to position each infrared-reflective silver layer ina low-emissivity coating directly over a pure zinc oxide layer.

While zinc oxide is beneficial for growing a high quality silver film,it has several drawbacks. One known drawback is that, because zinc oxideis a highly crystalline film, it is not particularly dense. Thus, purezinc oxide layers tend to be less than ideal for preventing air,moisture, sodium ions, and other materials from migrating through thezinc oxide layers and potentially reaching and reacting with the silverlayers. Further, when zinc oxide is deposited by sputtering, it tends toexhibit pinholes more frequently than would be ideal. Great care istaken to avoid pinholes, as they can also give air, moisture, and otherchemicals access to the silver layers. Another drawback of zinc oxide isthat thick zinc oxide layers tend to exhibit more stress than ispreferred. This can result in less than optimal adhesion, hence creatingthe potential for delamination. Notwithstanding these drawbacks, it isconventional in the art to provide pure zinc oxide directly beneath eachsilver layer in a low-emissivity coating.

It would be desirable to provide a low-emissivity coating that achievesbetter durability than conventional low-emissivity coatings wherein eachinfrared-reflective layer is pure silver. It would be particularlydesirable to provide a coating that achieves this result without anundue increase in emissivity.

SUMMARY OF THE INVENTION

The present invention is directed to a substrate bearing alow-emissivity coating. The coating comprises, in sequence outwardly(i.e., moving away from the substrate), a corrosion-resistant innerinfrared-reflective layer, a transparent dielectric middle coat, and anouter infrared-reflective layer. The outer infrared-reflective layerconsists essentially of silver and the corrosion-resistant innerinfrared-reflective layer has a different composition than the outerinfrared-reflective layer. Preferably, the transparent middle coatcomprises a layer consisting essentially of zinc oxide positioneddirectly beneath the outer infrared-reflective layer. This zinc oxidelayer typically has a thickness of at least about 40 Å.

In some cases, the inner infrared-reflective layer comprises acorrosion-resistant silver alloy. Preferably, the alloy comprises amajor portion of silver and a minor portion of a durable metal, thedurable metal being a metal other than silver. Perhaps optimally, atomsof the durable metal account for less than about 10 atomic percent ofthe total number of metal atoms in the inner infrared-reflective layer.Preferably, the durable metal is a metal selected from the groupconsisting of platinum, palladium, copper, nickel, gold, indium, zinc,silicon, boron and beryllium.

In other cases, the corrosion-resistant inner infrared-reflective layercomprises an electrically conductive nitride. Theelectrically-conductive nitride is preferably a nitride selected fromthe group consisting of chromium nitride, zirconium nitride, titaniumnitride, and niobium nitride.

In certain embodiments, the low-emissivity coating further comprises atransparent dielectric base coat between the substrate and thecorrosion-resistant inner infrared-reflective layer. This transparentbase coat typically comprises a durable transparent dielectric layerpositioned directly beneath the corrosion-resistant inner-infraredreflective layer. Preferably, the durable transparent dielectric layercomprises a desired metal other than zinc. This desired metal can be ametal selected from the group consisting of tin, aluminum, bismuth,indium, titanium, niobium, and silicon. In some cases, the durabletransparent dielectric layer comprises both zinc and the desired metal.For example, the durable transparent dielectric layer can comprise amajor portion of zinc oxide and a minor portion of an oxide of thedesired metal. Perhaps optimally, the durable transparent dielectriclayer comprises zinc tin oxide and/or zinc aluminum oxide. In somecases, atoms of the desired metal account for less than about 10 atomicpercent of the total metal atoms in the durable transparent dielectriclayer. In some embodiments, the low-emissivity coating further comprisesa transparent dielectric outer coat further from the substrate than theouter infrared-reflective layer.

In certain particularly preferred embodiments, the invention provides asubstrate bearing a low-emissivity coating comprising, in sequenceoutwardly, a transparent base layer, a transparent dielectric base coat,a corrosion-resistant inner infrared-reflective layer, a transparentdielectric middle coat, and an outer infrared-reflective layer. In theseembodiments, the outer infrared-reflective layer consists essentially ofsilver and the corrosion-resistant inner infrared-reflective layer has adifferent composition than the outer infrared-reflective layer. Here,the silicon dioxide is deposited directly over the substrate.Conjointly, the transparent dielectric base coat comprises at least onetransparent dielectric film. Further, the transparent dielectric middlecoat includes at least five transparent dielectric intermediate layers.Preferably, though not necessarily, the silicon dioxide has a thicknessof less than 100 Å. In some preferred embodiments, each of thetransparent dielectric intermediate layers has a thickness of less than200 Å. In some cases, all the preferred features described in thisparagraph are provided in combination and the transparent dielectricmiddle coat includes a layer consisting essentially of zinc oxidedirectly beneath the outer infrared-reflective layer and the transparentdielectric base coat includes a durable transparent dielectric layerdirectly beneath the corrosion-resistant inner infrared-reflectivelayer, the durable transparent dielectric layer comprising a desiredmetal, the desired metal being a metal other than zinc. In certainrelated methods, each layer/film described in this paragraph isdeposited by a conventional sputtering method.

The invention also provides methods of producing coated substrates,e.g., by depositing a low-emissivity coating on a substrate. Typically,the method comprises providing a substrate having a surface, anddepositing the low-emissivity coating onto this surface. Preferably,this involves depositing a low-emissivity coating comprising, movingoutwardly from the substrate, a corrosion-resistant innerinfrared-reflective layer, a transparent dielectric middle coat, and anouter infrared-reflective layer. Typically, the outerinfrared-reflective layer is deposited as a film consisting essentiallyof silver and the inner infrared-reflective layer is deposited as a filmhaving a different composition than the outer infrared-reflective layer.Preferably, the deposition of the transparent dielectric middle coatincludes depositing a layer consisting essentially of zinc oxidedirectly beneath the outer infrared-reflective layer. In some cases,this zinc oxide layer is deposited at a thickness of at least about 40angstroms. In certain favored methods, the middle coat is formed bydeposited at least five intermediate films (as described). In some ofthe present embodiments, the inner infrared-reflective layer isdeposited as a film comprising a corrosion-resistant silver alloy. Forexample, the inner infrared-reflective layer can be deposited as a filmcomprising a major portion of silver and a minor portion of a durablemetal, the durable metal being a metal other than silver. Here, theinner infrared-reflective layer is preferably deposited as a filmwherein atoms of the durable metal account for less than about 10 atomicpercent relative to the total number of metal atoms in the innerinfrared-reflective layer. In some cases, the inner infrared-reflectivelayer is deposited as a film comprising silver and a durable metalselected from the group consisting of platinum, palladium, copper,nickel, gold, indium, zinc, silicon, boron, and beryllium. The innerinfrared-reflective layer can alternatively be deposited as a filmcomprising an electrically-conductive nitride. When this is done, thedeposition of the middle coat can optionally include depositing an oxideor nitride layer directly over the electrically-conductive nitride ofthe inner infrared-reflective layer. In some cases, the innerinfrared-reflective layer is deposited as a film comprising anelectrically-conductive nitride selected from the group consisting ofchromium nitride, zirconium nitride, titanium nitride, and niobiumnitride. If so desired, the present method can further comprisedepositing a transparent dielectric base coat between the substrate andthe corrosion-resistant inner infrared-reflective layer, the transparentdielectric base coat including a durable transparent dielectric layerdirectly beneath the corrosion-resistant inner infrared-reflectivelayer, the durable transparent dielectric layer comprising a desiredmetal, the desired metal being a metal other than zinc. For example, thedurable transparent dielectric layer can be deposited as a filmcomprising a desired metal selected from the group consisting of tin,aluminum, bismuth, indium, titanium, niobium, and silicon Preferably,the durable transparent dielectric layer is deposited as a filmcomprising zinc and the desired metal. For example, the durabletransparent dielectric layer can be deposited as a film comprising amajor portion of zinc oxide and a minor portion of an oxide of thedesired metal. In some cases, the durable transparent dielectric layeris deposited as a film wherein atoms of the desired metal account forless than about 10 atomic percent relative to the total number of metalatoms in the durable transparent dielectric layer. Perhaps optimally,the durable transparent dielectric layer is deposited as a filmcomprising zinc tin oxide and/or zinc aluminum oxide. In some cases, themethod further comprises depositing a transparent dielectric outer coatfurther from the substrate than the outer infrared-reflective layer.Preferably, each layer in the coating is deposited on the substrate bysputtering.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a coating in accordancewith certain embodiments of the present invention;

FIG. 2 is a schematic cross-sectional view of a coating in accordancewith certain embodiments of the invention; and

FIG. 3 is a schematic cross-sectional view of a coating in accordancewith certain embodiments of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The following detailed description is to be read with reference to theFigures, in which like elements in different Figures have like referencenumerals. The Figures, which are not necessarily to scale, depictselected embodiments and are not intended to limit the scope of theinvention. Skilled artisans will recognize that the examples providedherein have many useful alternatives that fall within the scope of theinvention.

The present invention provides a corrosion-resistant low-emissivitycoating for glass and other substrates. It has been discovered that theouter infrared-reflective layer in a “double-type” low-emissivitycoating has a far greater impact on the total emissivity of the coatingthan does the inner infrared-reflective layer. In fact, the impact ofthe inner infrared-reflective layer on the coating's emissivity issurprisingly small. Thus, in a coating of the present invention, theinner infrared-reflective silver layer is replaced with a layer of amore durable (particularly more corrosion resistant) infrared-reflectivematerial. Surprisingly, the present coating achieves a substantialincrease in overall coating durability (particularly in corrosionresistance) with very little increase in overall coating emissivity.

The invention provides a substrate 10 bearing a corrosion-resistantlow-emissivity coating 40. A variety of substrates are suitable for usein the present invention. In most cases, the substrate is a sheet oftransparent material (i.e., a transparent sheet). However, the substrateis not required to be transparent. For example, opaque substrates may beuseful in some cases. However, it is anticipated that for mostapplications, the substrate will comprise a transparent or translucentmaterial, such as glass or clear plastic. In many cases, the substratewill be a glass pane. A variety of known glass types can be used, andsoda-lime glass is expected to be preferred.

FIG. 1 depicts an alternate embodiment of the present coating 40,wherein the coating comprises, in sequence outwardly (i.e., moving awayfrom the substrate) a corrosion-resistant inner infrared-reflectivelayer 50, a transparent dielectric middle coat 90, and an outerinfrared-reflective layer 150. Thus, the outer infrared-reflective layer150 is further from the substrate 10 than the transparent dielectricmiddle coat 90, and the transparent dielectric middle coat 90 is furtherfrom the substrate 10 than the corrosion-resistant innerinfrared-reflective layer 50. These layers need not be provided in acontiguous sequence, as will be apparent in view of the ensuingdiscussion.

FIG. 2 depicts certain preferred embodiments wherein the coating 40further comprises a base coat 30 and an outer coat 130. While the base30 and outer 130 coats are optional, both are preferred. Thus, incertain preferred embodiments, the coating 40 comprises, in sequenceoutwardly, a transparent dielectric base coat 30, a corrosion-resistantinner infrared-reflective layer 50, a transparent dielectric middle coat90, an outer infrared-reflective layer 150, and a transparent dielectricouter coat 130. Again, these layers need not be contiguous.

For example, FIG. 3 depicts certain preferred embodiments wherein thecoating 40 further comprises protective layers 80 and 180 positionedover the infrared-reflective layers 50 and 150, respectively. In thesepreferred embodiments, the coating 40 comprises, in sequence outwardly,a transparent dielectric base coat 30, a corrosion-resistant innerinfrared-reflective layer 50, a first protective layer 80, a transparentdielectric middle coat 90, an outer infrared-reflective layer 150, asecond protective layer 180, and a transparent dielectric outer coat130. Here again, the layers are not required to be contiguous. Rather,other layers can be interposed among these layers, if so desired. Incertain embodiments, though, these layers are provided in a contiguoussequence.

While certain preferred embodiments are detailed in this disclosure, itwill be apparent to skilled artisans that the present low-emissivitycoating 40 can be provided in many different layer structures eachcomprising the corrosion-resistant infrared-reflective layer 50, thetransparent dielectric middle coat 90, and the outer infrared-reflectivelayer 150.

In the present coating 40, the inner infrared-reflective layer 50 has adifferent composition (i.e., is formed of a different material) than theouter infrared-reflective layer 150. In particular, the outerinfrared-reflective layer 150 consists essentially of silver, whereasthe inner infrared-reflective layer 50 does not. Instead, the innerinfrared-reflective layer comprises at least one metal (i.e., the“durable” metal) other than silver. In some embodiments, the innerinfrared-reflective layer 50 comprises a corrosion-resistant silveralloy. In other embodiments, the inner infrared-reflective layer 50comprises an electrically conductive nitride. Embodiments of both typesare particularly preferred.

Thus, in some embodiments, the inner infrared-reflective layer 50comprises a corrosion-resistant silver alloy. Here, silver is providedin combination with (i.e., in an alloy comprising) at least one durablemetal. The durable metal can be a metal selected from the groupconsisting of platinum, palladium, copper, nickel, gold, indium, zinc,silicon, boron, and beryllium. Preferably, the inner infrared-reflectivelayer 50 comprises a major portion (i.e., at least 50 atomic percent) ofsilver and a minor portion (i.e., less than 50 atomic percent) of thedurable metal. For example, atoms of the durable metal preferablyaccount for less than about ten atomic percent of the metal atoms in theinner infrared-reflective layer 50. In other words, the percentage ofthe durable metal atoms relative to the total number of metal atoms inthis layer 50 preferably is less than about 10%. Perhaps optimally, theatomic percentage of the durable metal is less than about 1% (e.g.,between about 0.001% and about 1.0%). In embodiments wherein the innerinfrared-reflective layer 50 comprises silver and more than one durablemetal, the combined atomic percentage of the durable metals ispreferably within one or more of the foregoing ranges. Thus, in certainpreferred embodiments, the inner infrared-reflective layer 50 comprisesat least about 90 atomic percent (and perhaps optimally at least about99 atomic percent) silver and at least one durable metal at an atomicpercentage of less than about 10% (and perhaps optimally less than aboutone atomic percent).

In certain preferred embodiments, the inner infrared-reflective layer 50comprises a corrosion-resistant silver alloy selected from the groupconsisting of silver-copper, silver-nickel, and silver-titanium. Inthese embodiments, silver preferably is present in a major atomicpercentage (i.e., at least 50%, desirably at least about 90%, andperhaps optimally at least about 99%). While these silver alloys areadvantageous, the inner infrared-reflective layer 50 is not required tocomprise any particular silver alloy.

In one particular embodiment, the corrosion-resistant innerinfrared-reflective layer 50 comprises silver and copper (e.g., is asilver-copper alloy). In this embodiment, the inner infrared-reflectivelayer 50 preferably comprises a major portion of silver and a minorportion of copper. Useful silver-copper alloys are described in U.S.Pat. No. 4,462,883, the entire contents of which are incorporated hereinby reference. Here, the alloy contains 1% to 30% copper with theremainder being silver. Preferred silver-copper alloys are described inU.S. Pat. No. 4,883,721, the entire contents of which are incorporatedherein by reference. In this patent, the alloy contains 5% to 10% copperwith the remainder being silver. These particular alloys are preferredto silver-copper alloys that comprise more than 10% copper. Thus, incertain preferred methods, a metal alloy target formed of silver and1%-10% copper is sputtered (e.g., in an inert atmosphere) to deposit theinner infrared-reflective layer 50. Accordingly, it will be appreciatedthat in certain embodiments, the inner infrared-reflective layer 50consists essentially of silver and copper.

In other embodiments, the corrosion-resistant inner infrared-reflectivelayer 50 comprises (e.g., is an alloy of) silver and palladium. In theseembodiments, the inner infrared-reflective layer 50 preferably comprisesa major portion of silver and a minor portion of palladium. Usefulsilver-palladium alloys are described in U.S. Pat. No. 6,280,811, theentire contents of which are incorporated herein by reference. Here, themajor portion of silver is between about 85 atomic percent and about99.9 atomic percent and the minor portion of palladium is between about0.1 atomic percent and about 15 atomic percent. Preferably, the majorportion of silver is between about 89 atomic percent and about 99 atomicpercent and the minor portion of palladium is between about 1 atomicpercent and about 11 atomic percent. Thus, in certain preferred methods,a metal alloy target formed of between about 1 atomic percent and about11 atomic percent palladium (with the remainder being silver) issputtered (e.g., in an inert atmosphere) to deposit the innerinfrared-reflecting layer 50. Accordingly, it will be appreciated thatin certain embodiments, the inner infrared-reflective layer 50 consistsessentially of silver and palladium.

In some embodiments, the corrosion-resistant inner infrared-reflectivelayer 50 comprises (e.g., is an alloy of) silver, palladium, copper, andindium or zinc. In these embodiments, the inner infrared-reflectivelayer 50 preferably comprises a major atomic percentage of silver.Useful alloys of these metals are described in U.S. Pat. No. 5,037,708,the entire contents of which are incorporated herein by reference.Preferably, this alloy comprises 80% to 92.5% by weight silver, 4% to 9%by weight palladium, 2% to 10% by weight copper, and 0.5% to 1% byweight indium or zinc. Thus, in certain preferred methods, the layer 50is deposited by sputtering (e.g., in an inert atmosphere) a metal alloytarget formed of 80% to 92.5% by weight silver, 4% to 9% by weightpalladium, 2% to 10% by weight copper, and 0.5% to 1% by weight indiumor zinc. Accordingly, it will be appreciated that in certainembodiments, the inner infrared-reflective layer 50 consists essentiallyof silver, palladium, copper, and indium or zinc.

In other embodiments, the corrosion-resistant inner infrared-reflectivelayer 50 comprises (e.g., is an alloy of) silver and gold. In theseembodiments, the inner infrared-reflective layer 50 preferably comprisesa major portion of silver and a minor portion of gold. Usefulsilver-gold alloys are described in U.S. Pat. No. 6,280,811, the entirecontents of which are incorporated herein by reference. Preferably, thisalloy comprises between about 90 atomic percent and about 99.9 atomicpercent silver and between about 0.1 atomic percent and about 10 atomicpercent gold. More preferably, the major portion of silver is betweenabout 91.5 atomic percent and about 95 atomic percent and the minorportion of gold is between about 5 atomic percent and 9.5 atomicpercent. Thus, in certain more preferred methods, the layer 50 isdeposited by sputtering (e.g., in an inert atmosphere) a metal alloytarget formed of between about 91.5 atomic percent and about 95 atomicpercent silver and between about 5 atomic percent and about 9.5 atomicpercent gold. Accordingly, it will be appreciated that in certainembodiments, the inner infrared-reflective layer 50 consists essentiallyof silver and gold.

In some embodiments, the corrosion-resistant inner infrared-reflectivelayer 50 comprises (e.g. is an alloy of) silver, gold, and palladium. Inthese embodiments, the inner infrared-reflective layer 50 preferablycomprises a major portion of silver and minor portions of gold andpalladium. Useful alloys of this nature are described in U.S. Pat. No.6,280,811, the entire contents of which are incorporated herein byreference. Preferably, this alloy comprises between about 75 atomicpercent and about 99.8 atomic percent silver, between about 0.1 atomicpercent and about 10 atomic percent gold, and between about 0.1 atomicpercent and about 15 atomic percent palladium. More preferably, themajor portion of silver is between about 80.5 atomic percent and about94 atomic percent, the minor portion of gold is between about 5 atomicpercent and about 9.5 atomic percent, and the minor portion of palladiumis between about 1 atomic percent and about 10 atomic percent. Thus, incertain more preferred methods, the layer 50 is deposited by sputtering(e.g., in an inert atmosphere) a metal alloy target formed of betweenabout 80.5 atomic percent and about 94 atomic percent silver, betweenabout 5 atomic percent and about 9.5 atomic percent gold, and betweenabout 1 atomic percent and about 10 atomic percent palladium.Accordingly, it will be appreciated that, in certain embodiments, theinner infrared-reflective layer 50 consists essentially of silver, gold,and palladium.

In other embodiments, the corrosion-resistant inner infrared-reflectivelayer 50 comprises (e.g., is an alloy of) silver and beryllium. In theseembodiments, the inner infrared-reflective layer 50 preferably comprisesa major portion of silver and a minor portion of beryllium. Usefulalloys of this type are described in U.S. Pat. No. 6,280,811, the entirecontents of which are incorporated herein by reference. Preferably, thisalloy comprises between about 90 atomic percent and about 99.99 atomicpercent silver and between about 0.01 atomic percent and about 10 atomicpercent beryllium. More preferably, the major portion of silver isbetween about 94 atomic percent and about 99.9 atomic percent and theminor portion of beryllium is between about 0.1 atomic percent and about6 atomic percent. Thus, in certain more preferred methods, the layer 50is deposited by sputtering (e.g., in an inert atmosphere) a metal alloytarget formed of between about 94 atomic percent and about 99.9 atomicpercent silver and between about 0.1 atomic percent and about 6 atomicpercent beryllium. Accordingly, in certain embodiments, the innerinfrared-reflective layer 50 consists essentially of silver andberyllium.

In some embodiments, the corrosion-resistant inner infrared-reflectivelayer 50 comprises (e.g., is an alloy of) silver, zinc, copper, andsilicon. Useful alloys of this nature are described in U.S. Pat. No.5,882,441, the entire contents of which are incorporated herein byreference. Preferably, this alloy comprises 90% to 94% by weight silver,3.50% to 7.35% by weight zinc, 1% to 3% by weight copper, and 0.1% to2.5% by weight silicon. Thus, in certain preferred methods, the layer 50is deposited by sputtering (e.g., in an inert atmosphere) a metal alloytarget formed of 90% to 94% by weight silver, 3.50% to 7.35% by weightzinc, 1% to 3% by weight copper, and 0.1% to 2.5% by weight silicon.Accordingly, in certain embodiments, the inner infrared-reflective layer50 consists essentially of silver, zinc, copper, and silicon.

In some embodiments, the corrosion-resistant inner infrared-reflectivelayer 50 comprises (e.g., is an alloy of) silver, zinc, copper, nickel,silicon, and indium. Useful alloys of this nature are described in U.S.Pat. No. 5,817,195, the entire contents of which are incorporated hereinby reference. Preferably, this alloy comprises 90% to 92.5% by weightsilver, 5.75% to 7.5% by weight zinc, 0.25% to less than 1% by weightcopper, 0.25% to 0.5% by weight nickel, 0.1% to 0.25% by weight silicon,and 0.0% to 0.5% by weight indium. Thus, in certain preferred methods,the layer 50 is deposited by sputtering (e.g., in an inert atmosphere) ametal alloy target formed of 90% to 92.5% by weight silver, 5.75% to7.5% by weight zinc, 0.25% to less than 1% by weight copper, 0.25% to0.5% by weight nickel, 0.1% to 0.25% by weight silicon, and 0.0% to 0.5%by weight indium. Accordingly, it will be appreciated that in certainembodiments, the layer 50 consists essentially of silver, zinc, copper,nickel, silicon, and indium.

In some embodiments, the corrosion-resistant inner infrared-reflectivelayer 50 comprises (e.g., is an alloy of) silver, silicon, boron, zinc,copper, tin, and indium. Useful alloys of this nature are described inU.S. Pat. No. 5,039,479, the entire contents of which are incorporatedherein by reference. Preferably, this alloy comprises about 89% to 93.5%silver, about 0.02% to 2% silicon, about 0.001% to 2% boron, about 0.5%to 5% zinc, about 0.5% to 6% copper, about 0.25% to 6% tin, and about0.01% to 1.25% indium. Thus, in certain preferred methods, the layer 50is deposited by sputtering (e.g., in an inert atmosphere) a metal alloytarget formed of about 89% to 93.5% silver, about 0.02% to 2% silicon,about 0.001% to 2% boron, about 0.5% to 5% zinc, about 0.5% to 6%copper, about 0.25% to 6% tin, and about 0.01% to 1.25% indium.Accordingly, it will be appreciated that in certain embodiments, theinner infrared-reflective layer 50 consists essentially of silver,silicon, boron, zinc, copper, tin, and indium.

In other embodiments, the corrosion-resistant infrared-reflective layer50 comprises an electrically-conductive nitride. Preferred conductivenitrides include chromium nitride, zirconium nitride, titanium nitride,and niobium nitride. These nitrides are both reflective and electricallyconductive. The use of a conductive nitride for the innerinfrared-reflective layer 50 is particularly desirable, as the chemicalstability of the overall coating is greatly increased. When the innerinfrared-reflective layer is formed of a metallic film, it tends tooxidize when exposed to reactive oxygen. Nitride films tend to notoxidize as readily as metallic films. Therefore, in these embodiments,the coating 40 is particularly chemically stable, and will remainchemically stable over a particularly long period of time.

In embodiments wherein a conductive nitride is used for the innerinfrared-reflective layer 50, it is advantageous to omit the blockerlayer 80 that may otherwise be positioned over the innerinfrared-reflective layer 50. This blocker layer 80 can beadvantageously omitted in these embodiments since the innerinfrared-reflective layer 50 is formed of a relatively non-reactivenitride, rather than a highly reactive silver layer. Thus, a transparentdielectric film can be deposited (e.g., as an oxide or nitride) directlyover the inner infrared-reflective layer 50.

As noted above, in certain embodiments, the inner infrared-reflectivelayer 50 comprises at least one durable metal. The durable metal is ametal other than silver. For example, the durable metal can be platinum,palladium, copper, nickel, gold, indium, zinc, silicon, boron, andberyllium. In some alternate embodiments, the inner infrared-reflectivelayer 50 comprises one of these durable metals. For example, the innerinfrared-reflective layer 50 can be a film consisting essentially of anickel-based alloy that is corrosion resistant. Examples ofcorrosion-resistant nickel alloys include nichrome and nickel-aluminum.The term “nichrome” is used in its generic sense to designate a layercomprising some combination of nickel and chromium (e.g., 80% by weightnickel and 20% by weight chromium).

The inner infrared-reflective layer 50 preferably has a thickness ofbetween about 50 Å and about 250 Å, more preferably between about 50 Åand about 180 Å, and perhaps optimally between about 65 Å and about 180Å. Preferably, the outer infrared-reflective layer 150 is somewhatthicker than the inner infrared-reflective layer 50. For example,certain embodiments provide the inner infrared-reflective layer 50 at athickness of between about 50 Å and about 150 Å, more preferably betweenabout 58 Å and about 90 Å, and perhaps optimally about 80 Å, incombination with an outer infrared-reflective layer 150 at a thicknessof between about 90 Å and about 180 Å, more preferably between about 96Å and 155 Å, and perhaps optimally about 130 Å.

As noted above, the outer infrared-reflective layer 150 consistsessentially of silver (e.g., is pure or essentially pure silver).Preferably, this layer 150 is deposited as metallic silver. For example,the outer infrared-reflective layer 150 can be deposited by sputtering ametallic silver target in an argon atmosphere at a pressure of betweenabout 3×10⁻³ mbar and about 8×10⁻³ mbar. The outer infrared-reflectivelayer 150 preferably has a thickness of between about 50 Å and about 250Å, more preferably between about 50 Å and about 180 Å, and perhapsoptimally between about 65 Å and about 180 Å. By forming the outerinfrared-reflective layer 150 of silver, the present coating 40 isprovided with exceptionally low emissivity, surprisingly even though theinner infrared-reflective layer 50 is not formed of pure silver.

To minimize the emissivity of the outer infrared-reflective layer 150,this layer 150 is preferably (though not necessarily) positioneddirectly over a zinc oxide layer. Thus, the transparent dielectricmiddle coat 90 preferably includes a layer consisting essentially ofzinc oxide directly beneath the outer infrared-reflective layer 150.This facilitates the growth of silver having particularly low emissivityand particularly high visible transmission. The zinc oxide layer ispreferably deposited as pure (or essentially pure) zinc oxide. Forexample, this layer can be deposited by sputtering a metallic zinctarget in an argon/oxygen atmosphere at a pressure of between about4×10⁻³ mbar and about 8×10⁻³ mbar. The thickness of this zinc oxidelayer is desirably at least about 30 Å, more preferably at least about34 Å, and perhaps optimally at least about 40 Å (e.g., between about 40Å and about 250 Å). These minimum thicknesses are preferred to achievethe desired low emissivity and high visible transmission. However, it isnot necessary to form the entire transparent dielectric middle coat 90of zinc oxide. Rather, the middle coat 90 preferably (though notnecessarily) comprises a plurality of transparent dielectric layers.

The number of layers in the middle coat 90 can be varied as desired. Asnoted above, the layer directly beneath the outer infrared-reflectivesilver layer 150 preferably consists essentially of zinc oxide. Incertain embodiments, the middle coat 90 consists of a single layer ofzinc oxide. In these embodiments, the zinc oxide layer typically has athickness in the range of about 150-1200 Å. However, it is advantageousto include at least one amorphous or substantially amorphous layer(e.g., silicon nitride) in the middle coat 90. Amorphous layers areadvantageous in that they typically do not to experience major crystalgrowth when tempered or otherwise heat treated. As a result, they tendnot to develop objectionable haze due to large crystal growth duringheat treatment. Further, amorphous layers tend to be relatively denseand thus provide a good barrier to oxygen, nitrogen, moisture, and othermaterials that may become somewhat mobile in the coating 40. Therefore,it is desirable to provide a middle coat 90 that includes at least oneamorphous layer in combination with a layer of pure zinc oxide directlybeneath the outer infrared-reflective silver layer 150. Exemplary middlecoats 190 of this nature are described below.

Thus, in certain embodiments, the middle coat 90 comprises at least twotransparent dielectric layers. Whether the middle coat 90 consists ofone or multiple transparent dielectric layers, the optical thickness(i.e., the product of refractive index and physical thickness) of themiddle coat 90 preferably is about 300-2400 Å. In one embodiment, themiddle coat 90 comprises a silicon nitride layer and a zinc oxide layer,with the zinc oxide layer positioned over (i.e., outwardly from) thesilicon nitride layer and directly beneath the outer infrared-reflectivesilver layer 150. It is preferred to limit the thickness (e.g., to lessthan 200 Å) of each silicon nitride layer in the coating 40 to avoidundue stress. This is preferred because silicon nitride tends to havesignificant stress and because this stress tends to become moreproblematic as the thickness of each silicon nitride layer is increased.Particularly advantageous middle coat 90 designs are disclosed in U.S.patent application Ser. No. 09/728,435, the entire contents of which areincorporated herein by reference.

Thus, in certain embodiments, the middle coat 90 comprises a pluralityof transparent dielectric layers. For example, it is often preferred toform the middle coat 90 of at least three separate layers. In certainembodiments, the middle coat 90 includes a silicon nitride layerpositioned between two zinc oxide layers. In one embodiment of thisnature, the middle coat 90 comprises, moving outwardly from the optionalfirst blocker layer 80: (1) zinc oxide at a thickness of about 150-250Å, perhaps optimally about 220 Å; (2) silicon nitride at a thickness ofabout 40-120 Å, perhaps optimally about 80-100 Å; and (3) zinc oxide ata thickness of about 150-250 Å, perhaps optimally about 210 Å. It is notrequired that these three intermediate layers be contiguous. However,the middle coat 190 can advantageously consist of a contiguous sequenceof these three layers.

In certain preferred embodiments, the middle coat 90 comprises at leastfive transparent dielectric intermediate layers. In some embodiments ofthis nature, each of the transparent dielectric intermediate layers hasa thickness of less than 200 Å. Perhaps optimally, each transparentdielectric intermediate layer has a thickness of about 195 Å or less. Insome cases, the middle coat comprises alternating oxide and nitridelayers. In such cases, it is preferred for each intermediate nitridelayer to have a smaller thickness than each intermediate oxide layer.Preferably, the thickness of each intermediate nitride layer is lessthan about 180 Å, while the thickness of each intermediate oxide layermay range up to about 195 Å. In one embodiment, the middle coatcomprises alternating layers of a first, polycrystalline oxide (orsuboxide) and a second, substantially amorphous nitride. As one example,alternating layers of zinc oxide and silicon nitride can be used (e.g.,three layers of zinc oxide, two layers of silicon nitride). In oneembodiment, the middle coat 90 comprises, moving outwardly from theoptional first blocker layer 80: (1) a first intermediate layer formedof zinc oxide at a thickness of about 50-200 Å, perhaps optimally about105 Å; (2) a second intermediate layer formed of silicon nitride at athickness of about 50-200 Å, perhaps optimally about 140 Å; (3) a thirdintermediate layer formed of zinc oxide at a thickness of about 50-300Å, perhaps optimally about 200 Å; (4) a fourth intermediate layer formedof silicon nitride at a thickness of about 50-200 Å, perhaps optimallyabout 140 Å; and (5) a fifth intermediate layer formed of zinc oxide ata thickness of about 50-200 Å, perhaps optimally about 80 Å. While thesefive intermediate layers need not be contiguous, the middle coat canadvantageously comprise a contiguous sequence of these five layers.

In certain particularly advantageous embodiments, the low-emissivitycoating comprises, in sequence outwardly, a transparent base layer, atransparent dielectric base coat, a corrosion-resistant innerinfrared-reflective layer, a transparent dielectric middle coat, and anouter infrared-reflective layer. In these embodiments, the outerinfrared-reflective layer consists essentially of silver and thecorrosion-resistant inner infrared-reflective layer has a differentcomposition (described above) than the outer infrared-reflective layer.In these embodiments, the silicon dioxide is deposited directly over thesubstrate. Preferably, though not necessarily, the silicon dioxide has athickness of less than 100 Å (optimally between about 50 Å and about 90Å). The transparent dielectric base coat, which is deposited over thesilicon dioxide, comprises at least one transparent dielectric film. Inthe present embodiments, the transparent dielectric middle coat includesat least five transparent dielectric intermediate layers. In some cases,each of the transparent dielectric intermediate layers has a thicknessof less than 200 Å. In certain uniquely preferred embodiments, all thepreferred features described in this paragraph are provided incombination, and the transparent dielectric middle coat includes a layerconsisting essentially of zinc oxide directly beneath the outerinfrared-reflective layer and the transparent dielectric base coatincludes a durable transparent dielectric layer directly beneath thecorrosion-resistant inner infrared-reflective layer, the durabletransparent dielectric layer comprising a desired metal (describedbelow), the desired metal being a metal other than zinc. In certainrelated methods, each layer/film described in this paragraph isdeposited by a conventional sputtering method.

To maximize the durability of the present coating 40, thecorrosion-resistant inner infrared-reflective layer 50 is preferably(though not necessarily) positioned directly over a durable transparentdielectric layer comprising a metal other than zinc (preferably in atransparent dielectric compound that includes zinc and at least oneother metal). Thus, the layer directly beneath the corrosion-resistantinner infrared-reflective layer 50 preferably is not pure zinc oxide.This goes against conventional wisdom, as pure zinc oxide is stronglyfavored for use directly beneath each infrared-reflective layer in alow-emissivity coating. Surprisingly, the resulting durability, stress,and density benefits far outweigh the drawback of slightly increasedemissivity.

Preferably, the layer directly beneath the corrosion-resistant innerinfrared-reflective layer 50 comprises at least some tin, aluminum,bismuth, indium, titanium, niobium, and/or silicon. Of these desiredmetals, tin and aluminum are particularly preferred, and tin is uniquelypreferred. In certain preferred embodiments, this layer comprises anoxide of zinc in combination with (e.g., in a transparent dielectriccompound also comprising) an oxide of at least one other metal. Forexample, in certain particularly preferred embodiments, the innerinfrared-reflective layer 50 is deposited directly over a durabletransparent dielectric layer comprising a major portion of zinc oxideand a minor portion of an oxide of another metal (e.g., one of the“additional” or “desired” metals listed above in this paragraph).Preferably, atoms of the additional metal account for less than aboutten atomic percent relative to the total number of metal atoms in thedurable transparent dielectric layer. The additional metal oxide willslightly increase the emissivity of the inner infrared-reflective layer50, as compared to the emissivity of the layer 50 if it were depositeddirectly over pure zinc oxide. However, the impact of the innerinfrared-reflective layer 50 on the total emissivity of the coating 40is surprisingly small compared to the impact of the outerinfrared-reflective layer 150. Therefore, the use of a small amount ofanother metal oxide in a compound comprising zinc oxide will barely bedetectable in terms of increased coating emissivity. Moreover, when theadditional metal oxide is tin oxide or aluminum oxide (or a mixturethereof), the emissivity increase will be particularly small.

In the embodiments depicted in FIG. 2, the coating 40 includes all theelements of FIG. 1 and further includes a base coat 30 and an outer coat130. As noted above, the base coat 30 and the outer coat 130 areoptional, though preferred, in the present coating 40. In certainembodiments, the base coat 30 is provided directly over the surface 12of the substrate 10. In other uniquely preferred cases, a transparentbase layer (not shown) is formed directly over the surface 12 of thesubstrate 10 and the base coat 30 is formed directly over thetransparent base layer. In embodiments of this nature, the transparentbase layer is a silicon dioxide film having a thickness of less than 100Å (optimally between about 50 Å and about 90 Å). Particularlyadvantageous transparent base layers are described in U.S. patentapplication Ser. No. 10/087,662, the entire contents of which areincorporated herein by reference.

In its simplest form, the preferred base coat 30 consists of a singletransparent dielectric layer. When only a single layer is used, the basecoat 30 is preferably a durable transparent dielectric layer of the typedescribed above. Thus, in certain preferred embodiments, the base coat30 is a single transparent dielectric layer comprising an oxide of zincand at least one other metal. For example, the single transparentdielectric layer can comprise at least some tin, aluminum, bismuth,indium, titanium, niobium, and/or silicon. In certain embodiments ofthis nature, the base coat 30 is a single zinc tin oxide layer, or asingle zinc aluminum oxide layer, positioned directly beneath thecorrosion-resistant inner infrared-reflective layer 50.

In other embodiments, the base coat 30 comprises a plurality oftransparent dielectric layers. When a plurality of transparentdielectric layers are used, the layer directly beneath thecorrosion-resistant inner infrared-reflective layer 50 preferably is adurable transparent dielectric layer of the type described above. Thus,in certain preferred embodiments, the base coat 30 comprises multipletransparent dielectric layers including at least one durable transparentdielectric layer comprising a metal other than zinc, (e.g., comprisingat least some tin, aluminum, bismuth, indium, titanium, niobium, and/orsilicon). In certain preferred embodiments of this nature, the base coat30 includes at least one durable transparent dielectric layer comprisingzinc tin oxide and/or zinc aluminum oxide. In these embodiments, thedurable transparent dielectric layer preferably is directly beneath theinner infrared-reflective layer 50.

The base coat 30 can comprise any number of transparent dielectriclayers. Whether the base coat 30 consists of one or multiple transparentdielectric layers, the optical thickness of the base coat 30 preferablyis between about 150 Å and about 1200 Å. The term “transparentdielectric” is used herein to refer to any non-metallic (i.e., neither apure metal nor a metal alloy) compound that comprises any one or moremetals and is substantially transparent when applied as a thin film.Included in this definition would be any metal oxide, metal nitride,metal carbide, metal sulfide, metal boride, etc. (and any combinationsthereof, such as oxynitrides). Exemplary metal oxides include oxides ofzinc, tin, indium, bismuth, titanium, hafnium, zirconium, and mixturesthereof. Metal oxides tend to be advantageous due to their ease and lowcost of application. However, metal nitrides (e.g., silicon nitride) canalso be used quite advantageously. The term “metal” is to be understoodto include all metals and semi-metals (i.e., metalloids), such assilicon.

With continued reference to FIG. 2, the present coating 40 preferablyincludes an outer coat 130 positioned further from the substrate 10 thanthe outer infrared-reflective layer 150. The preferred outer coat 130comprises at least one transparent dielectric layer. In its simplestform, the preferred outer coat 130 consists of a single transparentdielectric layer. A wide variety of transparent dielectric films can beused as the outermost layer of the present coating 40. Preferably, achemically and mechanically durable material is used when the outer coat130 is a single layer. For example, certain embodiments employ an outercoat 130 formed by a single layer of silicon nitride, titanium dioxide,or tin oxide, each of which offers relatively good chemical andmechanical durability.

In certain embodiments, the outer coat 130 comprises a plurality oftransparent dielectric layers. Whether the outer coat 130 consists ofone or multiple transparent dielectric layers, the optical thickness ofthe outer coat 130 preferably is between about 150 Å and about 1200 Å. Avariety of film stacks are well known by skilled artisans to be suitablefor use as the outer coat of a low-emissivity coating, and any such filmstack can be used as the outer coat 130 of the present coating 40.

It may be preferable to limit each layer of the outer coat 130, as wellas each layer of the base 30 and middle 90 coats, to a physicalthickness of no more than about 250 Å, more preferably no more thanabout 225 Å, and perhaps optimally less than 200 Å. Moreover, it ispreferred if each layer in the outer coat 130, as well as each layer inthe base 30 and middle 90 coats, is formed of a different material thaneach layer contiguous thereto. As described in U.S. patent applicationSer. No. 09/728,435, this is believed to reduce the likelihood thatobjectionable haze will develop in the coating during heat treatment.

In certain embodiments (not shown), the outer coat 130 comprises atleast two transparent dielectric layers. For example, a first outerlayer can be deposited directly upon the optional second blocker layer180 and a second outer layer can be deposited directly upon this firstouter layer. The first outer layer can be formed of any desiredtransparent dielectric material, such as zinc oxide. The thickness ofthe first outer layer is preferably between about 25 Å and about 300 Å,more preferably between about 50 Å and about 275 Å, and perhapsoptimally between about 70 Å and about 250 Å. The second outer layer canbe formed of any desired transparent dielectric material, although it ispreferably formed of material having good chemical and mechanicaldurability. For example, this layer can be advantageously formed ofsilicon nitride. The thickness of the second outer layer is preferablybetween about 25 Å and about 300 Å, more preferably between about 50 Åand about 275 Å, and perhaps optimally between about 70 Å and about 250Å. In one preferred embodiment, the first outer layer is formed of zincoxide at a thickness of about 175 Å and the second outer layer is formedof silicon nitride at a thickness of about 75 Å. In another preferredembodiment, the first outer layer is formed of zinc oxide at a thicknessof about 225 Å and the second outer layer is formed of silicon nitrideat a thickness of about 96 Å.

In the embodiments depicted in FIG. 3, the coating 40 includes all theelements of FIG. 2 and further includes protective (or “barrier” or“blocker”) layers 80, 180 positioned directly over theinfrared-reflective layers 50 and 150, respectively. The protectivelayers 80, 180 are preferred, though not strictly required, in thecoating 40.

The protective layers 80, 180 are preferably provided to protect theunderlying infrared-reflective layers from chemical attack and toprovide resistance to deterioration (e.g., oxidation) of theinfrared-reflective layers during deposition of subsequent layers and/orduring heat treatment. An additional or alternative purpose for eachprotective layer may be to enhance the adhesion of the next-appliedlayer to the underlying infrared-reflective film. Moreover, theprotective layers 80, 180 can be provided as stress-reducing layers insome embodiments (e.g., wherein the protective layers comprisenickel-chromium compounds). Further, the thickness of the protectivelayers 80, 180 can be varied to adjust the color and/or shadingproperties of the coating 40.

Each protective layer can be deposited as a layer comprising a metalselected from the group consisting of titanium, niobium, nickel, andchromium. Further, skilled artisans may wish to select other knownmaterials for use in the protective layers 80, 180. The protectivelayers 80, 180 are preferably each applied at a thickness of about 7-30Å, more preferably about 15-22 Å, and perhaps optimally about 20 Å.

Any conventional method can be used to deposit the layers of the presentcoating 40. Preferably, each layer is deposited by sputtering.Sputtering techniques and equipment are well known in the present art.For example, magnetron sputtering chambers and related equipment arecommercially available from a variety of sources (e.g., Leybold and BOCCoating Technology). Useful magnetron sputtering techniques andequipment are also disclosed in U.S. Pat. No. 4,166,018 (Chapin), theentire teachings of which are incorporated herein by reference.

Generally speaking, magnetron sputtering involves providing at least onetarget formed of material to be deposited upon a substrate. In thisprocess, a clean substrate (e.g., glass) is placed in a coating chamber,which is evacuated (commonly to a pressure of less than 10⁻⁴ torr, morecommonly to less than 2×10⁻⁵ torr). Typically, the target is providedwith a negative charge and a relatively positively charged anode ispositioned adjacent the target. By introducing a relatively small amountof a desired gas into the chamber (commonly at a pressure rangingbetween about 1-30 mtorr), a plasma of that gas can be established.Particles (e.g., ions) in the plasma collide with the target, ejectingtarget material from the target and sputtering it onto the substrate. Tofacilitate this process, it is known to position magnets behind thetarget to shape and focus the plasma about a sputtering surface of thetarget.

In certain embodiments, the invention provides methods of producingcoated substrates, e.g., by depositing a corrosion-resistantlow-emissivity coating onto a substrate. The method typically comprisesproviding a substrate having a desired surface (e.g., a major surface)and depositing a low-emissivity coating of the type described above ontothe desired surface. Typically, the method comprises depositing upon thedesired surface a low-emissivity coating comprising, in sequenceoutwardly, an optional base coat 30, a corrosion-resistant innerinfrared-reflective layer 50, an optional first blocker layer 80, atransparent dielectric middle coat 90, an outer infrared-reflectivelayer 150, an optional second blocker layer 180, and an optional outercoat 130. The method comprises depositing the outer infrared-reflectivelayer 150 as a film consisting essentially of silver and depositing thecorrosion-resistant inner infrared-reflective layer 50 as a film havinga different composition than the outer infrared-reflective layer 150.Preferably, the corrosion-resistant inner infrared-reflective layer 50is deposited as a film comprising at least one metal other than silver.For example, this layer 150 can be advantageously deposited as a filmcomprising at least one durable metal selected from the group consistingof platinum, palladium, copper, nickel, gold, indium, zinc, silicon,boron, and beryllium. In more detail, the inner infrared-reflectivelayer 50 can be advantageously deposited as a corrosion-resistant silveralloy, e.g., comprising a major atomic percentage of silver and a minoratomic percentage of at least one metal other than silver). Each layerin the low-emissivity coating 40 preferably is deposited by sputtering.

One exemplary coating 40 will now be described. Directly upon a majorsurface of a glass sheet was deposited a zinc tin oxide layer. This zinctin oxide layer had a thickness of about 147 Å. Directly upon this layerof zinc tin oxide was deposited a silver alloy layer comprising silverand palladium. The silver alloy layer had a thickness of about 60-70 Å.Directly upon the silver alloy layer was deposited a layer of titanium.This titanium layer was deposited at a thickness of about 17-23 Å.Directly, upon this layer of titanium was deposited a layer of zincoxide. This zinc oxide layer was deposited in an oxidizing atmosphereand therefore the underlying titanium layer was partially oxidized. Thiszinc oxide layer had a thickness of about 175 Å. Directly upon thislayer of zinc oxide was deposited a layer of silicon nitride. Thissilicon nitride layer had a thickness of about 70 Å. Directly upon thislayer of silicon nitride was deposited another layer of zinc oxide. Thiszinc oxide layer had a thickness of about 130-140 Å. Directly upon thislayer of zinc oxide was deposited another layer of silicon nitride. Thissilicon nitride layer had a thickness of about 105 Å. Directly upon thislayer of silicon nitride was deposited another layer of zinc oxide. Thislayer of zinc oxide had a thickness of about 187 Å. Directly upon thiszinc oxide layer was deposited a layer of silver. The layer of silverhad a thickness of about 117 Å. Directly upon the layer of silver wasdeposited another layer of zinc oxide. This zinc oxide layer had athickness of about 175 Å. Finally, directly upon this zinc oxide layerwas deposited a layer of silicon nitride. This silicon nitride layer(which was the outermost layer of the coating) had a thickness of about75 Å.

Another exemplary coating 40 will now be described. Directly upon amajor surface of a glass sheet was deposited a layer of silicon dioxide.The silicon dioxide layer had a thickness of about 60 Å. Directly uponthe layer of silicon dioxide was deposited a layer of zinc tin oxide.This layer of zinc tin oxide had a thickness of about 140 Å. Directlyupon this layer of zinc tin oxide was deposited a silver alloy layercomprising silver and palladium. The silver alloy layer had a thicknessof about 71 Å. Directly upon the silver alloy layer was deposited aprotective layer of niobium. This protective layer of niobium had athickness of about 18 Å. Directly upon this protective layer of niobiumwas deposited a layer of zinc oxide. This layer of zinc oxide wasdeposited at a thickness of about 105 Å. Directly upon this layer ofzinc oxide was deposited a layer of silicon nitride. This siliconnitride layer had a thickness of about 124 Å. Directly upon this layerof silicon nitride was deposited another layer of zinc oxide. This zincoxide layer was deposited at a thickness of about 124 Å. Directly uponthis layer of zinc oxide was deposited another layer of silicon nitride.This silicon nitride layer had a thickness of about 124 Å. Directly uponthis layer of silicon nitride was deposited another layer of zinc oxide.This zinc oxide layer had a thickness of about 113 Å. Directly upon thislayer of zinc oxide was deposited a layer of silver. The silver layerhad a thickness of about 116 Å. Directly upon on the layer of silver wasdeposited a protective layer of niobium. This layer of niobium had athickness of about 18 Å. Directly upon this layer of niobium wasdeposited a layer of zinc oxide. This layer of zinc oxide had athickness of about 100 Å. Directly upon this layer of zinc oxide wasdeposited a layer of silicon nitride. This layer of silicon nitride hada thickness of about 40 Å. Directly upon this layer of silicon nitridewas deposited a layer of titanium nitride. The layer of titanium nitridehad a thickness of about 16 Å. Directly upon the layer of titaniumnitride was deposited a layer of silicon nitride. This layer of siliconnitride (which was the outermost layer of the coating) had a thicknessof about 122 Å.

While there have been described what are believed to be preferredembodiments of the present invention, those skilled in the art willrecognize that other and further changes and modifications can be madewithout departing from the spirit of the invention, and all such changesand modifications should be understood to fall within the scope of theinvention.

1. A substrate bearing a low-emissivity coating comprising, in sequenceoutwardly, a corrosion-resistant inner infrared-reflective layer, atransparent dielectric middle coat, and an outer infrared-reflectivelayer, wherein the outer infrared-reflective layer consists essentiallyof silver and the corrosion-resistant inner infrared-reflective layerhas a different composition than the outer infrared-reflective layer.